In mining and construction, excavating equipment ordinarily include a series of spaced apart teeth mounted across the digging edge of the excavator (e.g. the lip of a bucket). The teeth project forwardly to engage and break up the material to be gathered in the bucket. As can be appreciated, the teeth are subjected to highly abrasive conditions and experience considerable wearing.
In order to minimize the throw away material from used replacement parts, the teeth are manufactured of multiple parts, including an adapter and a point. The adapter is attached to the bucket's lip and includes a forwardly projecting nose. The point includes a front digging end and defines a rearwardly opening socket into which the adapter nose is received. In this way, the point substantially envelops the adapter nose. The point is therefore subjected to abrasive conditions and must be frequently replaced. The points must be securely locked to the adapters to withstand the heavy loading, but still be easily set and released for replacement of points in the field. The locking pin must also be able to withstand any of the environmental conditions to which the teeth are exposed, preferably including potentially corrosive conditions such as working in salt water.
In general, the point and adapter nose are provided with complimentary locking apertures for receiving a locking pin. A wide variety of point-adapter nose configurations are possible. A few examples are described in U.S. Pat. No. 5,469,648, which is incorporated by reference in its entirety. When the parts are assembled, the apertures are aligned to enable receipt of a locking pin. In some cases, a rigid pin is used in combination with a resilient keeper member. The keeper member is employed to hold the pin in the apertures and to tighten the engagement of the point over the adapter nose. In an alternative arrangement, a sandwich pin is used without a separate keeper member. In general, a sandwich pin has a pair of a rigid portions which are combined with a resilient portion in an integral construction such that the pin works to secure the point in place and tighten the connection of the parts.
While sandwich pins offer the convenience of using a single locking part, forming a pin with a cohesive, durable construction can be a problem. For instance, the resilient portion and the metal portion are typically fixed together with an adhesive to maintain the pin as a single part. There is great reliance therefore on the adhesive bond between the pieces. However, adhesives can fail in corrosive environments resulting in detachment of the pieces of a locking pin and loss of the pin.
During use, the pin is continuously loaded causing the metal portion to move against the resilient portion in a cyclic manner. The resilient material can lose its resilience through fatigue failure due to continuous loading so that the material is not sufficiently expansive to hold the pin in the aligned apertures. Loss of the pin results in a lost point, which, in turn, exposes the adapter to premature wear and possible damage to the equipment receiving the overburden with the lost point.
The continuous loading can also have an adverse effect on the adhesive bond between the resilient portion and the metal portion resulting in a fatigue failure of the bond.
In most lock assemblies employing sandwich pins, the elastomeric element in the pin must expand to maintain a tight fit in the aligned assembly apertures and prevent loss of the pin. Once the maximum expansion of the elastomer member is reached, the pin may be lost or ejected. Therefore, in order to maximize the life of the components the apertures defined through the point and adapter nose, irrespective of whether they are vertical or horizontal apertures, are typically constructed so that the pin is initially inserted into a very tight arrangement.
In order to keep the elastomer element and the rigid elements of the pin together, most sandwich pin components are manufactured by inserting the rigid metal elements into a mold, coating an adhesive on the metal elements and then injection molding the elastomer element. This injection molding method is typically labor intensive requiring manual placement of the metal elements into the mold, molding and then removing the part from the mold. In addition to the manual positioning, molding, and removing steps, this manufacturing method requires cleaning of the part where primer and adhesive were coated on the metal elements, and also cleaning the flashing and sprues from the part.
U.S. Pat. No. 5,469,648 to Jones, et al. discloses an excavating tooth secured together with a sandwich lock pin. The lock pin includes a rigid casing formed with one or two cavities for receiving elastomeric material and metal coverings which overlay the elastomeric material to prevent premature wearing. The cavities into which the coverings are received, however, are too shallow to retain the coverings during use. Consequently, adhesive or the like is required to secure the coverings against loss. A failure of the adhesive due to corrosion or fatigue will result in a failure of the pin and loss of the point or other wear member.
U.S. Pat. No. 2,772,492 to Murtaugh discloses a retaining key for securing the adapter of a dipper tooth to a lip of a bucket. The retaining key comprises a C-shaped member, a wedge and a resilient pad interposed between them. Although the wedge has projections which are received into recesses the recesses are laterally open on one side. As a result, there is no provision for laterally constraining the wedge within the casing. During installation and use the wedge could slide out the side of the casing and be lost.